Question
The diagram shows the tandem repeats on two different chromosomes for a couple and their children. The number of tandem repeats of the sequence AGAT is shown on chromosome 5 (Chr 5) and the sequence of AGAA on chromosome 18 (Chr 18). One child is adopted.
(a) Outline the use of tandem repeats in DNA profiling.
(b) Identify the child that is adopted, giving a reason for your answer.
(c) Explain the function of a promoter in DNA.
▶️Answer/Explanation
(a) a. number of repeats (may) differ between individuals / is inherited (by children);
b. separation/bands produced by gel electrophoresis;
c. multiple sites/tandem repeats needed/used to produce a (unique) profile/fingerprint;
d. pattern/combination of bands (on gel)/of tandem repeats is unique to individuals;
e. used in forensics/criminal investigations/paternity testing;
(b) child 1/the boy as neither parent has 12 tandem repeats on chromosome 5;
(c) a. is a non-coding/non-transcribed section of DNA/bases;
b. transcription starts/is initiated at the promoter;
c. region for binding (to DNA) of RNA polymerase
OR
region for RNA polymerase to separate the DNA strands;
d. located upstream of the gene/coding sequence;
e. helps to control/regulate gene expression;
Question
▶️Answer/Explanation
Question
b.i. State one role of nucleosomes in eukaryotic cells.[1]
b.ii. Outline how Hershey and Chase’s experiment provided evidence for DNA as the genetic material. [3]
b.iii. State one function for a region of DNA that does not code for proteins. [1]
c.i. Outline the role of the A-site of ribosomes in translation. [1]
c.ii. Outline the role of tRNA activating enzymes in translation. [2]
▶️Answer/Explanation
Markscheme
a. help to supercoil/pack DNA in chromosomes
b. help to regulate transcription / gene expression
a. experiment is meant to determine whether DNA or protein is the genetic material
b. viruses/bacteriophages grown in radioactive S/S35 which enters the protein coat
c. viruses/bacteriophages grown in radioactive P/P32 which enters the DNA
d. «radioactive» viral DNA entered the bacterial cell during infection
OR
«radioactive» viral protein did not enter the bacterial cell during infection
regulator of gene expression/introns/telomeres/genes for tRNA / rRNA / promoter / enhancer / silencer / site for primer to bind / codes for mRNA primer
binding/entry of tRNA carrying amino acids/aminoacyl tRNA / charged tRNA / site of transfer of growing polypeptide chains/peptide bond formation
a. ATP «hydrolysis» provides energy for amino acid attachment ✔
b. they attach a specific amino acid to the (3′) end / free CCA of a tRNA ✔
c. they do this repeatedly / they attach amino acid to all of the tRNA molecules that have anticodon corresponding to that amino acid